A cigarette typically includes a tobacco rod and a filter connected to the tobacco rod. The filter is commonly made of cellulose acetate tow. A smoker ignites one end of the tobacco rod and draws smoke in through the filter. The filter traps some of the smoke products produced by the burning tobacco rod. In some cases, the filter can be arranged to impart additional characteristics to the cigarette such as flavour.
US patent application US-A-2003/0224918 describes a device for applying a flavourant bearing element along the central axis of a cigarette filter during the filter manufacturing process. The preferred flavoured element is cotton yarn, but other suggested materials for the flavoured element are cellulose acetate, rayon, or some other textile or non-textile materials capable of absorbing a liquid flavourant. UK patent application GB-B-2020158 describes a similar filter to that disclosed in US-A-2003/0224918. A thread or tape, for example cotton sewing thread or rayon, extends along a filter rod. A flavourant is incorporated into the filter rod.
Although a cotton thread absorbs flavour during manufacturing and then imparts flavour during smoking, it does have certain drawbacks as a flavourant. For example, the cotton thread may become discoloured as a result of smoke passing through the filter. One option to avoid such discolouration is to apply a dye to the cotton thread (where the colour of the dye would mask any discolouration). However, standard vat dyes for cotton are primarily intended for use with clothing; they generally do not have regulatory approval for food products (or for cigarettes, which are inserted into the mouth). In addition, the dye applied to cotton material may not be entirely colour-fast, and may therefore leach into the surrounding filter material. This is especially a problem if the cotton thread is exposed to a substance which may act as a solvent.